Question: Multiply.
Solution: When a number is next to a variable, it means they are multiplied. So, $({-4}{x^2})({7}{x^3})$ is the same as $({-4})({x^2})({7})({x^3})$. Now we can rearrange the factors because multiplication is commutative (a fancy way of saying that the order in which we multiply things doesn't matter). ${(-4)(7)}{(x^2)(x^3)}$ Then simplify, and we're done! ${-28}{x^5}$